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Here is a problem that pops up from time to time. The adhesive that is used to fasten the Hall sensor to the mounting bracket on the motor board of the video drum assembly picks up moisture, degrades and becomes conductive. When this happens the hall sensor can't tell the motor IC which phase the rotor is in so it stops dead. Here's how it works and why things go haywire when the sensor fails or shorts out. Looking to the right in the picture notice the six windings in what is called a pancake motor (called the stator the manuals). The part that turns is the armature (called the rotor). It is shown just behind it (dark gray disk). It has six fields of opposing polarities made into it. To make everything turn the windings of the stator must turn off and on in pairs of three to pull at the six fields in the rotor. The Hall sensor (which is a type of semiconductor that reacts to a magnetic field) senses the changes in polarity as the fields in the rotor go by it. The change tells an integrated circuit to turn the fields off and on in the proper sequence for the proper speed (controlled by electronics). If it can't sense any rotation everything stops and the stator magnetically locks in place. It acts like it wants to move but it can't and is free when the motor is not on. In some Beta units this also shuts down the machine. Click on the picture and you get a better look at the sensors and the stator mounting fixture. Click again and you see a repair being made when the sensor is still good. Cleaning away of the old adhesive and re-mounting the sensor restores operation. Click on the photo once again and here we have a repair when replacement was necessary. The last photo in the series shows the drum assembled and repaired. (All the photos show the drum upside down.)
To proceed to the next section that describes the EXTERNAL CLEANING AND RENEW click here.
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